A huge market exists for disk drives for mass-market computing devices such as desktop computers and laptop computers, as well as small form factor (SFF) disk drives for use in mobile computing devices (e.g. personal digital assistants (PDAs), cell-phones, digital cameras, etc.). To be competitive, a disk drive should be relatively inexpensive and provide substantial capacity, rapid access to data, and reliable performance.
Disk drives typically employ a moveable head actuator to frequently access large amounts of data stored on a disk. One example of a disk drive is a hard disk drive. A conventional hard disk drive has a head disk assembly (“HDA”) including at least one magnetic disk (“disk”), a spindle motor for rapidly rotating the disk, and a head stack assembly (“HSA”) that includes a head gimbal assembly (HGA) with a moveable transducer head for reading and writing data. The HSA forms part of a servo control system that positions the moveable transducer head over a particular track on the disk to read or write information from and to that track, respectively.
Typically, a conventional hard disk drive includes one or more disks wherein each disk includes a plurality of concentric tracks. Each surface of each disk conventionally contains a plurality of concentric data tracks angularly divided into a plurality of data sectors. In addition, special servo information may be provided on each disk to determine the position of the moveable transducer head. The moveable transducer head typically includes a writer and a reader.
The most popular form of servo is called “embedded servo” wherein the servo information is written in a plurality of servo sectors that are angularly spaced from one another and are interspersed between and within data sectors around each track of each disk. Each servo sector typically includes at least a phase locked loop (PLL) field, a servo sync mark (SSM) field, a track identification (TKID) field, a sector ID field having a sector ID number to identify the sector, and a group of servo bursts (e.g. an alternating pattern of magnetic transitions) that the servo control system of the disk drive samples to align the moveable transducer head with or relative to a particular track. Typically, the servo control system moves the transducer head toward a desired track during a “seek” mode using the TKID field as a control input. Once the moveable transducer head is generally over the desired track, the servo control system uses the servo bursts to keep the moveable transducer head over that track in a “track follow” mode.
In recent years, disks have begun utilizing a structured function called discrete track media (DTM). In the DTM structure, there are regions that are utilized as magnetic recording portions, referred to as lands, and ineffective regions between the lands, referred to as grooves. The lands are projection magnetic regions provided with a magnetic film. On the other hand, the grooves are on non-magnetic regions or depressed regions in which magnetic recording cannot be performed.
In DTM structures, the tracks are physically printed, stamped, or etched, into the disk so that physical grooves separate the data regions or track lands. Data can only be recorded on the track lands. Since the reader reads and aligns to the servo sectors on the track lands, it is generally a straight forward task to align the reader to the lands. More difficult is aligning the writer to the lands.
Standard heads having a reader and a writer are used with the DTM disk for data storage and retrieval in which there is a physical separation between the reader and the writer. The physical separation in combination with the rotary actuator gives rise to an offset between the reader and the writer such that the reader and writer are following two different tracks (except at zero skew). On continuous media, this phenomenon gives rise to “read jog.” Tracks are written at a nominal writer position and the head is jogged, moved over several tracks, to align the reader with the written track during readback operations. The underlying assumption is that the tracks can be defined by the normal position of the writer, without regard to the position of the media. DTM breaks this assumption.
With DTM, the tracks are physically printed, stamped or etched into the disk, so that physical grooves separate the track lands. Data and servo sectors can only be recorded on the track lands. Since the reader can easily read aligned servo sectors on the track land, it is an easy task to align the reader to the track lands. However, the position of the writer is difficult to align to the track land, since the servo sectors only provide information about how the reader is aligned to track lands. Thus the head must be jogged, moved over several tracks by a write jog distance, to align the writer with the physical tracks, before a track is written. Due to the grooves between the track lands and the various uncertainties and differences between the lengths of track lands and grooves during the manufacture of the DTM structure, aligning the writer to the track lands is a very difficult process.
Therefore, there is a need to determine write jog values in order to properly align the writer to track lands for writing operations for disks having DTM structures.